Fix lcov line mismatch errors in coverage generation

Add error suppression flags to handle template-heavy C++ code:
- --ignore-errors gcov,source,mismatch for lcov capture
- --ignore-errors source for genhtml generation

These flags resolve line number mismatches that occur with compiler
optimizations and template instantiations in complex C++ codebases.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <[email protected]>

Author: kkaefer

.github/workflows/build.yml

@@ -118,8 +118,9 @@ jobs:
           # Create coverage directory
           mkdir -p coverage
 
-          # Capture coverage data
-          lcov --capture --directory build --output-file coverage/coverage_raw.info
+          # Capture coverage data with error suppression for template-heavy code
+          lcov --capture --directory build --output-file coverage/coverage_raw.info \
+            --ignore-errors gcov,source,mismatch --gcov-tool gcov
 
           # Remove system headers, vendor files, and test files from coverage
           lcov --remove coverage/coverage_raw.info '/usr/*' --output-file coverage/coverage.info
@@ -132,7 +133,9 @@ jobs:
           lcov --extract coverage/coverage.info '*/include/*' --output-file coverage/coverage.info
 
           # Generate HTML report
-          genhtml coverage/coverage.info --output-directory coverage/html --title "Earcut.hpp Coverage Report" --legend
+          genhtml coverage/coverage.info --output-directory coverage/html \
+            --title "Earcut.hpp Coverage Report" --legend \
+            --ignore-errors source
 
           # Show summary
           lcov --summary coverage/coverage.info